The present invention relates to a method of manufacturing a printed wiring or circuit board more particularly, it relates to a method of manufacturing a cubic or three-dimensional printed wiring board.
There are a variety of conventional methods of manufacturing a printed wiring board based on a cubically molded substrate including the double-shot process, transfer process, and the etching process for example. Of these, the etching process is executed either by forming etching resist via a pad printing means or by forming etching resist by exposing and developing photo-resist by applying a cubic mask.
According to the conventional double-shot process, palladium catalyzer is uniformly dispersed in a resinous region (of the cubic substrate) available for forming circuits, and then the resinous region is molded. Next, in order to secure those regions formed by the first and second molds, only the region available for forming circuits is externally expose before being molded. No catalyzer is added to the resinous region subject to molding by the second mold.
Next, the molded substrate is subject to a preliminary treatment by applying chromic acid so that the surface of the molded substrate can be roughed, followed by the execution of an electrolysis-free copper plating process before eventually forming printed circuits in the predetermined region.
The conventional transfer process uses transfer papers. More specifically , a transfer film that superficially contains a conductive circuit pattern is preliminarily set to a resin mold available for molding cubic substrate, and then, via the molding process, the circuit pattern of the transfer film is transferred onto the molded substrate. There is another conventional process for plating a circuit pattern in a mold in addition to the above process. In particular, this conventional process provides slits corresponding to circuit pattern inside of an extrusion mold, and then coats the surface of the mold other than the slits with resist by applying a roller printing method. Next, a metallic layer is formed solely on the slits by applying an electrolytic metal plating process. Next, the resist is removed from the mold surface and then an extrusion molding process is executed by means of an extrusion mold. Finally, the circuit pattern composed of a metallic layer electrolytically deposited on the mold surface is transferred onto the molded substrate.
Among the transfer processes, there is such a conventional process for transferring the predetermined circuit pattern onto the molded substrate. More specifically, circuit pattern is printed on a transfer film across a screen, and then, the circuit pattern is coated with an adhesive agent. Next, the circuit pattern of the transfer film is brought into contact with the transfer-receptive region of the molded substrate by precisely matching both positions. Next, the molded substrate is heated and pressed until the coated adhesive agent becomes fully solidified. Finally, after stripping off the transfer film, the circuit pattern is already on the transfer-receptive region of the molded substrate, thus completing the whole transfer process.
When applying the conventional etching process, initially, the surface of a cubically molded substrate is processed so as to have an adequate roughness. Next, a metallic layer available for composing a circuit conductor is coated o the whole surface of the cubically molded substrate by electrolytic and non-electrolytic plating processes. Next, etching resist corresponding to the predetermined circuit pattern is formed, and finally, the metallic layer is etched to complete the formation of the predetermined circuit pattern on the surface of the cubically molded substrate.
Conventionally, there are two ways of forming the etching resist during the manufacturing process. One of these method forms the etching resist by transferring resist ink to the surface of metallic layer by applying a pad printing process. The other method forms the etching resist by initially coating the whole surface of the metallic layer with liquid photo-resist, by applying either a dipping process or a spraying method, followed by processes for exposing and developing the coated photo-resist across a cubic mask before eventually forming the etching resist.
When forming printed circuits on a cubically molded substrate by applying the conventional double-shot process mentioned earlier, there is a certain restriction on the selection of material available for the initial molding process, in the compatibility with a palladium catalyzer. In addition, there is also a certain restriction on the resinous material available for implementing the first and second molding processes due to consideration of thermal compatibility. Furthermore, since the mold is quite expensive, the conventional double-shot process is by no means economical. In addition, there is a certain limit in terms of applicable line width (0.2 mm), interval (0.2 mm) and critical pitch (0.4 mm) which are respectively essential for the manufacture of the mold. Since there is a critical limit in the total length of circuits, the designing of circuits is limited.
Furthermore, when applying the conventional transfer process with transfer papers, each transfer operation against the cubic substrate having complex configuration is very difficult. In addition, it is difficult to form the cubically molded substrate and it is also difficult to provide precise correct positions for the circuit patterns. In particular, the plating of the circuit pattern in the mold expensive on the way of manufacturing the mold. Furthermore, since the circuit pattern is plated in the mold, the line width and the interval are respectively restricted to 0.2 mm. Furthermore, a plating process must be executed against the mold whenever molding the objective substrate, thus diminishing the availability for implementing mass production.
On the other hand, the conventional method of transferring the circuit pattern subsequent to the molding of the substrate also involves difficulty in following the complex configuration of the cubic substrate. Also, the circuit pattern is bonded to the substrate with adhesive agent, creating a problem with regards to the peeling strength.
Furthermore, when applying the conventional etching process to form the etching resist based on the pad printing process, difficulty is also present in following the complex configuration of the cubic substrate. In addition, there is a certain limit in the line width and the interval of circuits, also, it is difficult to provide a durable thickness of etching resist. Furthermore, the conventional etching process is defective because of an inability to design through holes in the circuit pattern.
On the other hand, when forming the etching resist from photo-resist, it is difficult to uniformly coat liquid photo-resist on the whole surface of a cubic substrate without causing pin holes to occur. It is also difficult to form a cubic photo-mask that correctly matches the configuration of the cubic substrate. This makes the production process very costly. Furthermore, there is a critical limit in the formation of pattern containing fine conductive lines.